The present invention relates to a method for heating powder material and an apparatus for carrying out said method. More particularly the invention relates to a method for preheating and/or calcining powder and an apparatus for carrying out said method.
It is well known that powder material such as a cement raw material is calcined and sintered in a furnace such as rotary kiln or the like after completion of preheating. There is a variety of apparatus for preheating, calcining and sintering, for instance, apparatus consisting of preheater and rotary kiln. Recently an apparatus with a preheater having a flash furnace (calcining furnace) annexed thereto has been proposed and has been used. This conventional apparatus is such that preheating and/or calcining of powder material is carried out with the use of hot gas coming from the rotary kiln or the like, but it is recognized as a disadvantage with the conventional apparatus that heat exchanging between hot gas and powder material takes place in less number of times, resulting in reduced thermal efficiency. For instance, in case of four stage type preheating apparatus, heat exchanging takes place only in four times at low thermal efficiency.
To eliminate the drawbacks with the hitherto known apparatus and method, there was proposed method wherein hot gas coming from single hot gas source is divided into two or more branch flows, heat exchanging takes place between the branch flows and raw material to be heated and then the waste hot gas in branch flows is again united and exhausted with the aid of single blower (c.f. Japanese Patent Publication No. 22855/64). This method brings about increased number of times of heat exchanging between raw material and hot gas, but it is found out therewith that thermal efficiency is not so good mainly because of single hot gas source. Moreover it is pointed out as another drawback with the aforesaid method that since there is provided a single inlet for supply of raw material to be heated, gas flow in the hot gas passage in which the raw material charged is cooled down but other gas flow with no raw material charged therein remains hot, causing thermal efficiency not only to be reduced but also temperature and pressure at the blower to be controlled with much difficulty. Furthermore since the waste hot gas in two or more branch flows is united in a duct and exhausted with the aid of a single blower, it becomes necessary to control pressure and temperature difference in the respective branch flows by means of a pressure control dumper of the like mounted in said branch flow, which not only causes considerably high pressure loss but also increased size of the blower.